Is there a way to force MacOS 14.1 to use SMB 2?

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Level 4

1,510 points

Is there a way to force MacOS 14.1 to use SMB 2?

MacOS 14.0/14.1 broke the ability of Macs to connect to our institution's NAS. The institution's NAS only supports SMB 1/2/3, and specifically for SMB 3, it's SMB 3.0 only. But MacOS 14.0/14.1 uses SMB 3.1.1, and that fails when trying to connect to the institution's SMB 3.0 NAS.

Windows 11 has the same problem, but there's a Window Registry that allows you to set the maximum negotiated SMB version — in this case from SMB 3.1.1 to SMB 3.0. And with that Registry entry, the Windows 11 SMB clients have no problem connecting to the institution's NAS.

Unfortunately, there is no corresponding MaxNegotiatedSMB setting in MacOS' /etc/nsmb.conf file.

Furthermore, there appears to be no way in MacOS' /etc/nsmb.conf file to limit SMB to SMB 2.

In other *nix implementations, protocol_vers_map= can have arguments of 1, 2, & 3, corresponding to SMB 1, SMB 2, SMB 1/2.

But the MacOS 14.1 man pages for the nsmb.conf entry protocol_vers_map=, list only 4, 5, & 6, corresponding to SMB 3, SMB 2/3, & SMB 1/2/3 as valid arguments. And this seems to be deliberate, because any of:

protocol_vers_map=1

protocol_vers_map=2

protocol_vers_map=3

seem to have no effect if entered into MacOS 14.1's /etc/nsmb.conf file.

Posted on Oct 27, 2023 10:04 AM

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Answer 1

Ben Schmidt Author

Level 4

1,510 points

Nov 15, 2023 1:20 PM in response to Ben Schmidt

My institutional SAN head only supports SMB 1, 2, and 3, but not SMB 3.1.1, which MacOS 14 uses when it tries to connect to SMB 3-compliant storage.

To force MacOS 14.1 to use SMB 2 as a temporary workaround, I had unsuccessfully tried using an /etc/nsmb.conf file, containing just these two lines:

[default]

protocol_vers_map=2 #force SMB to v2

With the help of Google and a colleague, I then tried, instead, using these 7 lines in /etc/nsmb.conf:

[default]

signing_required=no

streams=yes

notify_off=yes

port445=no_netbios

protocol_vers_map=2

signing_req_vers=0

...And success! My MacOS 14.1 can now once again, connect to my institutional SAN, as it could pre-MacOS 14 update.

The result is an SMB 2 connection, which is less secure than SMB 3.1.1, but as a temporary fix, until my institution upgrades their institutional SAN to support SMB 3.1.1, a connection is better than none. 👍

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